J. K. Smith wrote:
> I've tried a lot of ways but nothing has worked so far.
> The following statements are my problem simplified:
>
> f[x_] := 2x^3;
> ParametricPlot[{D[f[x], x], x^2}, {x, 0, 1}]
>
> When I run this I get error messages griping about numbers not being
> valid variables but it doesn't end up plotting anything. In this example
> I should see a straight line.
>
> I've tried using Evaluate[ D[f[x],x] ] and lots of other schemes which
> seemed to work in the past but I can't get ParametricPlot to digest any
> of them. Something about the result of that derivative doesn't yield
> something that can be plotted. But I don't know what property it is.
>
> Would you kind Mathematica gurus please get me thru this one (too)?
f[x_] := 2*x^3;
g[x_] = D[f[x], x];
ParametricPlot[{g[x], x^2},
{x, 0, 1}]
Note that this approach doesn't work if you use delayed assignment :=
instead of immediate assignment = in the definition of g[x].
I'm not sure why using Evaluate doesn't work.
--
Curt Fischer